Pump piston



FIG. 1 shows an exploded side view of my claimed design of which the other side view is identical;

FIG. 2 shows a front view of my claimed design;

FIG. 3 shows a rear view of my claimed design;

FIG. 4 shows a front perspective view of my claimed design; and,

FIG. 5 shows a rear perspective view of my claimed design. 

The ornamental design for a pump piston, as shown and described. 